When murine L cells are deprived of essential nutrients they cease proliferating and dramatically change the relative rates at which they synthesize several abundant cytoplasmic proteins. One of the affected proteins, a 94,000 molecular weight polypeptide from the soluble cytoplasm (designated S-94), has been purified and shown to be a single molecular species by a variety of standard criteria. The major objectives of the proposed studies are: 1) determine the variations in culture conditions that are capable of altering the pattern of major proteins synthesized; 2) determine whether changes in rate of synthesis of these proteins are accompanied by changes in intracellular distribution; 3) examine the relationship between the pattern of protein synthesis and the ability to initiate DNA synthesis and 4) determine the mechanism by which the rate of synthesis of these cytoplasmic proteins in general and of S-94 in particular is regulated. These studies will contribute to understanding the regulation of cell proliferation in a variety of pathological conditions.